Introduction

Abstract

The mid-1960s witnessed two fundamental revelations that resulted in the beginning of an era which continues to have profound effects on the geologic sciences. Although the basic ideas of continental drift had been proposed nearly a half century earlier by Alfred Wegener, it was not until the late 1950s and early 1960s and the development of modern instruments to measure sea-floor spreading, to date rocks radiometrically, and to conduct accurate geophysical surveys, that the concept of crustal plate tectonics was accepted. At the same time as the gradual acceptance of plate tectonics, a similar, equally profound, view of the Solar System was emerging. Just as the ideas of continental drift were hampered by the lack of data, Solar System studies were also limited until the space age. Prior to the return of results from space probes sent to the Moon and planets, views of most planetary objects (except the Moon) were limited to little more than fuzzy blurs or tiny pin-points of light, even when viewed with the most powerful Earth-bound telescopes (Fig. 1.1).